From a recent tube collection that was stored away for many years and recently acquired side triangle = Heerlen, Netherlands please see up close of codes. â9â =1959 or 1969 â Kâ = November Maxi-preamp 2 tester Test great and closely matched triodes: Gain 48.4 / 49.9 (3.1 % delta) Gm 2894 / 2815 (2.8% delta) Pass noise, pass microphonics Beautiful and NOS